Bridge drive diagnostic system

ABSTRACT

A diagnostic system for determining the existence of bridge tracking problems related to a relative difference of drive speeds of independent bridge drive motors on a crane. The diagnostic system includes at least one drive speed measurement unit (e.g., tachometer) that is utilized to measure the drive speed of each of the independent bridge drive motors on the crane. Generally, each drive speed is measured from the drive shaft and/or the drive wheel. The measured drive speeds are compared to determine if the relative difference is great enough to cause bridge tracking problems. The diagnostic system is portable and therefore usable on a plurality of cranes.

BACKGROUND OF THE INVENTION

[0001] The invention relates to overhead cranes that operate on spaced apart rails. More particularly, the invention relates to a diagnostic system for a bridge drive of an overhead crane that observes and records the relative drive speeds of independent bridge drive motors.

[0002] Common overhead cranes are driven by two or four independent bridge drive motors. A crane with two independent bridge drive motors includes a first drive wheel and a first idler wheel, each adapted to roll along a first rail, and a second drive wheel and a second idler wheel, each adapted to roll along a second rail. Bridge tracking problems are introduced when the relative speed between a drive shaft driving the first drive wheel and a second drive shaft driving the second drive wheel differ. When the relative drive speeds differ, the bridge (the frame or structure supporting the wheels) tends to want to travel faster down one rail than it does down the other rail, resulting in skewing of the bridge. A crane with four independent bridge drive motors includes four drive wheels that are each driven by a separate drive motor. In addition to the skewing problems discussed above, a crane with four independent bridge drive motors may experience problems associated with small speed differences between drive wheels on the same side of the bridge manifesting themselves as small amounts of tread slippage and accelerated wheel wear.

[0003] There are many known causes of bridge tracking problems and methods of diagnosing such problems. For example, runway misalignment is diagnosed with a runway survey; an out of square bridge frame is diagnosed with a parallel wire survey; bridge wheel misalignment is diagnosed with a parallel wire survey; incorrect bridge wheel-to-wheel span is diagnosed with a parallel wire survey; worn bridge wheels are visually inspected; the skidding/breaking traction is visually observed; and drive wheel diameter tolerances are directly measured. However, systematic or engineered methods or devices to diagnose differences in the drive speeds of drive motors are not available.

SUMMARY OF THE INVENTION

[0004] Accordingly, the invention provides a diagnostic system for directly observing and recording the relative drive speeds of each independent bridge drive motor under actual operating conditions. The invention can eliminate or minimize relative drive speed differences as a cause of bridge tracking problems when other causes are suspected.

[0005] In one embodiment, the invention provides a method of diagnosing bridge tracking problems related to a relative difference of drive speeds of independent bridge drive motors on a crane. The method includes measuring the drive speed of each independent bridge drive motor on the crane, comparing the measured drive speeds, determining the relative difference of the drive speeds, and assessing if the relative difference of the drive speeds is the cause of the bridge tracking problems.

[0006] In another embodiment, the invention provides a portable bridge drive diagnostic system for a crane. The diagnostic system includes drive speed measurement units that are coupled to measure the drive speeds produced by each of the independent bridge drive motors on the crane. Each drive speed measurement unit is coupled to either the drive shaft or the drive wheel driven by each of the independent bridge drive motors of the crane. The diagnostic system also includes a data acquisition unit for recording the measured data that is coupled to each of the drive speed measurement units.

[0007] Other features and advantages of the present invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings in which like numerals are used to designate like features.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the drawings:

[0009]FIG. 1 is a perspective view of a representative overhead traveling crane.

[0010]FIG. 2 is a plan view of the crane of FIG. 1.

[0011]FIG. 3 is a view taken along line 3-3 of FIG. 2.

[0012]FIG. 4 is a plan view of a crane and illustrates one embodiment of the invention.

[0013]FIG. 5 is a schematic representation of a data acquisition unit coupled to drive speed measurement units.

DETAILED DESCRIPTION

[0014] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

[0015] Before describing the invention, it will be helpful to have an understanding of how a representative overhead traveling crane 10 is configured. FIG. 1 illustrates the crane 10 having a frame 14 with a pair of bridge cross-members 18 and 22, and trucks 26 and 30 at opposite ends of the bridge cross-members 18 and 22. An operator's cab 34 is suspended from the frame 14. The crane 10 may include either two or four independent bridge drive motors. For the sake of brevity, the crane 10 is illustrated as including only two independent bridge drive motors.

[0016]FIG. 2 further illustrates the crane 10 with two independent bridge drive motors. Drive wheels 36 and 40 are respectively rotatably mounted on the trucks 26 and 30 and engage rails 46 and 50, respectively, so that the rails support the crane 10. Additional non-driven or idler wheels 56 and 60 are respectively rotatably mounted on the trucks 26 and 30 and engage the rails 46 and 50, respectively, for further support of the crane 10. The rails 46 and 50 are respectively mounted on beams 66 and 70 (see FIG. 3) or other suitable foundation means. The rotatable engagement of the drive and idler wheels with the rails permits travel of the crane 10 along the rails.

[0017] Motors 76 and 80 are mounted on the frame 14 and drive the wheels 36 and 40, respectively. A hoist 84 (see FIG. 1) having a load hook 88 is supported for travel on tracks 92 and 96 which are respectively mounted on the cross-members 18 and 22 of the crane 10. The hoist 84 also includes motors (not shown) for moving the hoist along the tracks and for raising and lowering the load hook 88. The crane 10 may be operated by well-known controls, not shown, which control the operation of the motors 76 and 80, the movement of the hoist on the tracks, and the raising and lowering of the load hook 88. A crane with four independent bridge drive motors includes four drive wheels, two drive wheels in engagement with each rail, and four motors, one motor driving each of the four drive wheels.

[0018] As schematically illustrated in FIG. 4, drive speed measurement units 100 are coupled to the crane 10 in a manner that allows for measurement of a drive speed of each independent bridge drive motor. After the measurement is completed, the drive speed measurement units 100 are uncoupled from the crane 10. Preferably, simultaneous drive speed measurements are obtained for each independent bridge drive motor. However, the drive speed measurements may be made individually (i.e., one at a time) if the crane 10 is controlled in a similar manner during all measurements. Generally, the drive speed can be measured on the drive shaft and/or the drive wheel driven by each independent bridge drive motor, respectively. One method of measuring the drive speed is to use a tachometer. Preferably the tachometer is coupled to the drive shaft for measurement of the drive speed, although in another embodiment a tachometer can be coupled to the drive wheel. Commonly available tachometers (including hand held tachometers) are suitable for use in the invention. The tachometer may be coupled to the drive shaft or the drive wheel either mechanically, electrically, optically, or in any other known manner. Optical coupling a tachometer may include placing a reflective tape or a notch on the drive shaft or the drive wheel which provides a once-per-revolution indicator of the drive speed. All other methods of measuring the drive speed, either directly or indirectly, are applicable to this invention. Preferably, the drive speed measurement units 100 are easily fit onto the crane 10 for measurement. Measurements from existing drive speed measurement units 100 may be utilized in accordance with the invention if such hardware is preexisting on the crane 10.

[0019] As illustrated in FIG. 5, each of the drive speed measurement units 100 are connected to a data acquisition unit 110. In one embodiment, the respective drive speeds acquired are displayed on an optional display screen 115 for immediate analysis. In another embodiment the respective drive speeds are recorded, then later plotted and analyzed. The respective drive speeds are compared for relative differences. The analysis can include computing the amount of theoretical wheel slippage and skew angle, and assessment of the relative differences to determine if asynchronous drive speeds is a cause of the bridge tracking problems. The invention can thereby eliminate or minimize relative drive speed differences as a cause of bridge tracking problems when other causes are suspected. If it is determined during the assessment that asynchronous drive speeds are not the cause of the bridge tracking problems, the crane service provider can move on to examining other potential causes and be assured that asynchronous wheel speed is not a potential cause. Provision of the display screen 115 on the data acquisition unit 110 permits immediate observation of relative speeds in the field.

[0020] In one embodiment, the data acquisition unit 110 and the drive speed measurement units 100 are packaged as a single unit that is sufficiently small enough for placement to acquire the drive speed measurements. The single unit may include leads connected to the portion including the drive speed measurement units 100 for such placement.

[0021] The output of each drive speed measurement unit 100 can be either a series of data points (e.g., waveform), or a single value. The output may include a value of revolutions per minute (“RPM”), a voltage value, or any other value that is demonstrative of the drive speed.

[0022] In one embodiment, the invention indicates small differences in the respective drive speeds. If a relative difference is indicated, generally known methods of correcting the drive speeds are employed. On cranes 10 with two independent bridge drive motors, small differences in the respective drive speeds may result in skewing of the bridge. On cranes 10 with four independent bridge drive motors, small differences in the respective drive speeds may result in skewing and tread slippage which causes accelerated wheel wear.

[0023] The invention is preferably retrofit onto cranes that do not include the ability to independently measure the drive speeds produced by the crane's independent bridge drive motors. The invention is preferably applicable to crane service providers and is therefore portable and usable on a plurality of different cranes. Although the invention is preferably applicable to cranes, it can be used in other applications that include at least two independent drives which may have a relative difference between their respective drive speeds.

[0024] In one embodiment, the invention offers a direct method to compare respective drive speeds produced by each independent bridge drive motor and does not rely on analytical or theoretical methods. A direct measurement as discussed herein includes measuring or observing actual physical phenomena rather than analytically or formulaically arriving at a value for the physical phenomena.

[0025] Thus, the invention provides, among other things, a diagnostic system for directly observing and recording the relative drive speeds of each independent bridge drive motor under actual operating conditions. Various features and advantages of the invention are set forth in the following claims. 

What is claimed is:
 1. A method of diagnosing bridge tracking problems related to a relative difference of drive speeds of independent bridge drive motors on a crane, the method comprising the acts of: measuring the drive speeds of at least two independent bridge drive motors on the crane; comparing the measured drive speeds; determining the relative difference of the drive speeds of the at least two independent bridge drive motors; and assessing if the relative difference of the drive speeds is the cause of the bridge tracking problems.
 2. A method as set forth in claim 1, and further comprising the act of coupling a drive speed measurement unit to at least one of a drive shaft and a driven wheel driven by one of the independent bridge drive motors on the crane, wherein the drive speed measurement unit is used to accomplish the act of directly measuring the drive speeds.
 3. A method as set forth in claim 2 wherein coupling a drive speed measurement unit includes coupling a tachometer to at least one of a drive shaft and a driven wheel driven by one of the independent bridge drive motors on the crane.
 4. A method as set forth in claim 3 wherein coupling a tachometer includes coupling a hand held tachometer to at least one of a drive shaft and a driven wheel driven by one of the independent bridge drive motors on the crane.
 5. A method as set forth in claim 2 wherein the act of coupling the drive speed measurement unit includes at least one of electrically coupling, mechanically coupling, and optically coupling the drive speed measurement unit to the at least one of a drive shaft and a driven wheel driven by the one of the independent bridge drive motors on the crane.
 6. A method as set forth in claim 2, and further comprising the act of uncoupling the drive speed measurement unit from the at least one of the drive shaft and the driven wheel driven by the one of the independent drive motors of the crane after the act of measuring the drive speeds.
 7. A method as set forth in claim 2, and further comprising the act of coupling the drive speed measurement unit to a data acquisition unit.
 8. A method as set forth in claim 7, and further comprising the act of recording the measured drive speeds, wherein the data acquisition unit is used to accomplish the act of recording the measured drive speeds.
 9. A method as set forth in claim 8, and further comprising the act of displaying and analyzing the measured drive speeds that are recorded.
 10. A method as set forth in claim 7 wherein the drive speed measurement unit and the data acquisition unit are portable.
 11. A method as set forth in claim 1, and further comprising the act of displaying the measured drive speeds.
 12. A method as set forth in claim 1 wherein the act of measuring the drive speeds is done substantially simultaneously.
 13. A method as set forth in claim 1 wherein the act of measuring the drive speeds includes directly measuring the drive speeds.
 14. A portable bridge drive diagnostic system for a crane, wherein the crane includes at least two independent bridge drive motors, the diagnostic system comprising: at least one drive speed measurement unit, wherein the at least one drive speed measurement unit is configured to be coupled to at least one of a drive shaft and a driven wheel driven by one of the at least two independent bridge drive motors on the crane, and wherein the at least one drive speed measurement unit is operable to produce an output signal; and a data acquisition unit configured to receive the output signal of the at least one drive speed measurement unit.
 15. A diagnostic system as set forth in claim 14 wherein the drive speed measurement unit is a tachometer.
 16. A diagnostic system as set forth in claim 15 wherein the tachometer is hand-held.
 17. A diagnostic system as set forth in claim 14 wherein the at least one drive speed measurement unit is configured to be electrically coupled to at least one of a drive shaft and a driven wheel driven by one of the at least two independent bridge drive motors on the crane.
 18. A diagnostic system as set forth in claim 14 wherein the at least one drive speed measurement unit is configured to be mechanically coupled to at least one of a drive shaft and a driven wheel driven by one of the at least two independent bridge drive motors on the crane.
 19. A diagnostic system as set forth in claim 14 wherein the at least one drive speed measurement unit is configured to be optically coupled to at least one of a drive shaft and a driven wheel driven by one of the at least two independent bridge drive motors on the crane.
 20. A method of servicing a crane that is experiencing bridge tracking problems which may be related to a relative difference of drive speeds of independent bridge drive motors on the crane, the method comprising the acts of: coupling portable drive speed measurement units to at least one of a drive shaft and a driven wheel driven by each one of the independent bridge drive motors on the crane; measuring the drive speeds of at least two independent bridge drive motors on the crane in a substantially simultaneous manner, wherein the portable drive speed measurement units are used to accomplish the act of measuring the drive speeds; coupling each of the drive speed measurement units to a data acquisition unit; recording the measured drive speeds, wherein the data acquisition unit is used to accomplish the act of recording the measured drive speeds; comparing the measured drive speeds; determining the relative difference of the drive speeds of the at least two independent bridge drive motors; assessing if the relative difference of the drive speeds is the cause of the bridge tracking problems; and uncoupling the drive speed measurement units from the at least one of the drive shaft and the driven wheel driven by the each one of the independent drive motors of the crane after the act of measuring the drive speeds.
 21. A method as set forth in claim 20 wherein coupling a drive speed measurement unit includes coupling a tachometer to at least one of a drive shaft and a driven wheel driven by one of the independent bridge drive motors on the crane.
 22. A method as set forth in claim 21 wherein coupling a tachometer includes coupling a hand held tachometer to at least one of a drive shaft and a driven wheel driven by one of the independent bridge drive motors on the crane.
 23. A method as set forth in claim 20 wherein the act of coupling the drive speed measurement unit includes at least one of electrically coupling, mechanically coupling, and optically coupling the drive speed measurement unit to the at least one of the drive shaft and the driven wheel driven by the one of the independent bridge drive motors on the crane.
 24. A method as set forth in claim 10 wherein the act of measuring the drive speeds includes directly measuring the drive speeds. 